The present invention relates to an improvement in an electronic watch in which the power consumption of a stepping motor is reduced.
The present invention will be explained on the basis of an embodiment applying the principles of the present invention to an analogue type electronic watch.
The display mechanism of an analogue type crystal watch heretofore used is generally constructed as shown in FIG. 1. The output of the motor comprising a stator 1, a coil 7 and a rotor 6 is transmitted to a fifth wheel 5, a fourth wheel 4, a third wheel 3 and a second wheel 2. Although not shown, the output is then transmitted to a cylindrical member, a cylindrical wheel, and a calendar mechanism whereby a second hand, a minute hand, an hour hand and a calendar are driven.
In the case of wrist watch, a load seen from the stepping motor is extremely small except for the time for switching the calendar, so that a torque of 10 g/cm in the second wheel is sufficient for the driving. However, when switching the calendar, a torque which is several times greater than this is required. The time required for switching the calendar within twenty-four hours operation per day is only at most about six hours. However, for the reasons described above in the mechanism according to the prior art, there is a problem that electric power which enables the calendar driving mechanism to be operated in a stable condition must always be supplied from a power supply.
FIG. 2 shows an electronic watch circuit construction according to the prior art. The signal of 32.768 KHZ from an oscillation circuit 10 is converted to one second signal by a frequency dividing circuit 11. The one second signal is converted to a signal having a width of 7.8 m sec and a period of 2 seconds by a pulse width combining circuit 12, and the signal along with a signal having the same period and pulse width but being dephased by one second are applied to the inputs 15 and 16 of inverters 13a and 13b. As a result, an inverted pulse which changes the direction of the current is applied to a coil 14 once every second, so that the rotor 6 magnetized in two poles rotates in one direction. FIG. 3 shows the current waveform therefor. In this manner, the drive pulse width of the present day electronic watch is set by the required maximum torque as its standard. Therefore, in the time interval which does not require a large torque, electric power is wasted. This has prevented a lower power consumption for the watch.